The man was pronounced dead after cops were called just before 10am on Saturday to a home in Hillingdon, west London.
At 3.30am on Sunday the Met Police arrested a man on suspicion of murder.
He remains in custody at a local police station.
“Officers were called shortly before 10:00hrs in Saturday, 15 July to a residential address on Station Road in Hayes following reports of a man found deceased.
“Officers and the London Ambulance Service attended. A man, aged in his mid-40s, was found with a slash wound; he pronounced dead the scene.
“His family has been informed.
“The death is currently being treated as unexpected and is under investigation.
“A post-mortem examination will be held in due course.
“At about 03:30hrs on Sunday, 16 July, officers arrested a man on suspicion of murder.
“He was taken to a west London police station where he remains in custody.
“Enquiries continue.”